Let me explain it to you.
sauna is a small room or house designed as a place to experience dry or wet heat sessions, or an establishment with one or more of these and auxiliary facilities.
A sauna session can be a social affair in which the participants disrobe and sit or recline in temperatures typically between 70°C (158 °F) and 100°C(212 °F). This induces relaxation and promotes sweating.
Saunas can be divided into two basic styles: conventional saunas that warm the air or infrared saunas that warm objects. Infrared saunas may use various materials in their heating area such as charcoal, active carbon fibers, and other materials.